The invention relates to an improved device for adjusting a dosage in a device for administering a product, for example an injection syringe for insulin in the form of a pen-shaped syringe for self-administration of insulin, referred to as a pen. The invention further relates to a limiting mechanism that prevents the adjustment of a dosage to be administered past a predetermined value. As an example for the invention, but not restrictive to the applications in administration devices, embodiments of such devices are described in the published patent application CH 703993 A2, which is herewith incorporated in full by reference.
In administration devices with product containers, e.g., an inserted cartridge that contains a product for several administrations, it is sometimes desirable to prevent a dosage from being preselected that exceeds the amount of product remaining in the cartridge. If such a dosage could be preselected, the user would assume that a corresponding dosage can be administered, whereas in fact only a part is administered. This is undesirable or even dangerous depending on the situation.
A means for solving this problem known from prior art is to count or measure the total as the sum of the administered dosages, with a limit stop preventing a further ejection or dosage selection as soon as the total corresponds to the volume nominally contained in the cartridge.
A drive mechanism for medicine administration devices is described in the published patent application WO 2004/078226 for example. This drive mechanism contains a housing, a dosage-setting sleeve and a two-part piston. In one embodiment, a driver sleeve moves downward along an inner part of the piston rod when a dosage is selected. The distance traveled corresponds to the ejection stroke of the piston necessary for the dosage. When a subsequent dosage is selected, the driver sleeve moves farther along the piston rod. The position of the driver sleeve thus corresponds to the quantity of medication still contained in the cartridge. When the driver sleeve reaches the end of the thread on the inner part of the piston rod and therefore can no longer rotate, this corresponds to an empty cartridge.
Another example is described in the published patent application U.S. Pat. No. 6,582,404, which shows a limiting mechanism for medication administration devices that prevents setting a dosage which exceeds the amount remaining in the cartridge. The administration device comprises a dosage-setting member which is moved away from a fixed limit stop by rotation relative to a driver when setting a dosage. The dosage-setting member is connected to the driver in such a manner that the former can be turned in one direction without moving the latter. The dosage is administered by turning back the dosage-setting member and thereby moving the driver. The rotating driver causes an ejection motion of the piston rod. The driver is provided with a track, the length of which corresponds to the quantity of medication contained in the cartridge. A track follower, which is connected to the dosage-setting member, runs in this track. Every time a dosage is selected, the track follower moves farther in the track. When the track follower reaches the end of the track, the dosage-setting member cannot be turned further and setting a dosage beyond the amount still remaining in the cartridge is prevented.
Another example of such a device is described in EP 0554996 and shows an injection device for administering liquids such as insulin into bodily tissue. This injection device contains a dosage-setting mechanism having a 1-ring and a 10-ring. A transmission member is provided for selectively coupling the one ring to the other so that they turn together only in selected sections during the dosage-setting. The set dosage is displayed by means of digits on the rings. The injection device further comprises a dosage-limiting mechanism, which limits the movement of a guide spindle for the intended piston motion in the cartridge, wherein projections in the plunger reach the end of grooves along the guide spindle and prevent a further movement. The dosage-limiting mechanism is provided separately from the dosage-setting mechanism.
Finally, WO 2006/086983 shows an example of a dosage-setting device for self-injection devices with a dosage-limiting mechanism having two rotating parts, wherein the first part turns continually while setting a dosage and the second part only turns part of the time by a selective coupling device after a defined rotational position has been reached. This has the effect that the second part turns discontinuously over a smaller angle than the first part. The rotation of the second part is then limited by a limit stop fixed to the housing, which prevents a dosage setting exceeding the remaining amount still present in the cartridge.
A disadvantage of dosage-setting devices for self-injection devices known from the prior art with a dosage-limiting mechanism is that such devices require considerable space and/or coupling mechanisms, which require control and negatively influence the limitation.
The problem of the present invention is to create a device for setting a dosage in an injection or infusion device for administering a product having a limiting mechanism that reliably, simply and space-effectively prevents the setting of a dosage to be administered beyond a predetermined value and also overcomes other disadvantages known from the prior art.
This problem is solved by the subject matter with the characteristics of claim 1.
Additional advantageous embodiments follow from the dependent claims.